5g core network optimized local handover

ABSTRACT

The invention relates to an access and a method performed by the access manager of transferring data in a wireless communication system comprising a control plane distributed over at least one first site and over at least one second site, wherein a session manager is arranged in the control plane of the second site and the access manager is arranged in the control plane of the first site, the first site being remote from the second site and located physically closer to a radio access network of the wireless communication system.

TECHNICAL FIELD

The invention relates to an access manager, and a method performed bythe access manager of transferring data in a wireless communicationsystem comprising a control plane distributed over at least one firstsite and over at least one second site, wherein a session manager isarranged in the control plane of the second site and the access manageris arranged in the control plane of the first site, the first site beingremote from the second site and located physically closer to a radioaccess network of the wireless communication system.

BACKGROUND

A key requirement for next generation of mobile networks is flexibilityto support multiple use cases with different network requirements.

Software Defined Networking (SDN) has been proposed for enabling asolution without the need for centralized user plane nodes and with astrict division between control plane and user plane.

FIG. 1 illustrates an Evolved Packet Core (EPC) network architecturebeing the core network in a Long Term Evolution (LTE) communicationsystem. A mobile device 10, such as a mobile phone, tablet, smart watch,etc., is referred to as a User Equipment (UE) and connects to a BaseStation (BS) residing in an Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) 11. In EPC terminology, the BS is called evolved NodeB (eNB). The BS is connected to a Mobility Management Entity (MME) 12which handles signalling related to mobility for E-UTRAN access, such ase.g. tracking and paging of the UE 10. In particular, the MME 12controls the setup and maintenance of GTP (“General Packet Radio ServiceTunnelling Protocol”) user plane tunnels between the BS and a PacketData Network Gateway (P-GW) 14 via a Serving Gateway (S-GW) 13. The P-GW14 acts as a global mobility anchor point towards IP networks 15 andincludes functions like Quality-of-Service (QoS) handling and chargingsupport. The S-GW 13 acts as a local mobility anchor point and includesfunctions like idle-mode buffering. Policy and charging is governed froma Policy and Charging Rules Function (PCRF) 16. A Home Subscriber Server(HSS) 17 is the prime database for subscription-related information.

A problem in the art is that whereas EPC can be seen as aone-size-fits-all network mainly optimized for mobile broadband, a 5Gcore network must be able to support many diverse use cases.

SUMMARY

An object of the present invention is to solve, or at least mitigate,this problem in the art and thus to provide an improved method of anaccess manager of transferring data in a wireless communication systemfor providing a flexible architecture being capable of handling the manydifferent 5G use cases.

This object is attained in a first aspect of the invention by a methodperformed by an access manager of transferring data in a wirelesscommunication system comprising a control plane distributed over atleast one first site and over at least one second site, wherein asession manager is arranged in the control plane of the second site andthe access manager is arranged in the control plane of the first site,the first site being remote from the second site and located physicallycloser to a radio access network of the wireless communication system.The method comprises receiving information regarding a mobility eventwhere access of a wireless communication device is being transferredfrom a source access point to a target access point, the access pointsbeing connected to said at least one first site, and providing one ormore UPFs serving the wireless communication device with informationidentifying the target access point and information identifying thewireless communication device, wherein the information is provided tothe one or more UPFs without passing the control plane of the secondsite. The method further comprises acquiring information indicating ifthe access manager is allowed to finish its mobility event procedurewithout informing the session manager that the access of the wirelesscommunication device is being transferred, and if so finishing themobility event procedure without informing the session manager that theaccess of the wireless communication device is being transferred.

This object is attained in a second aspect of the invention by an accessmanager configured to transfer data in a wireless communication systemcomprising a control plane distributed over at least one first site andover at least one second site, wherein a session manager is arranged inthe control plane of the second site and the access manager is arrangedin the control plane of the first site, the first site being remote fromthe second site and located physically closer to a radio access networkof the wireless communication system. The access manager comprises aprocessing unit and a memory, the memory containing instructionsexecutable by the processing unit, whereby the access manager isoperative to receive information regarding a mobility event where accessof a wireless communication device is being transferred from a sourceaccess point to a target access point, the access points being connectedto said at least one first site, provide one or more UPFs serving thewireless communication device with information identifying the targetaccess point and information identifying the wireless communicationdevice, wherein the information is provided to the one or more UPFswithout passing the control plane of the second site, and acquireinformation indicating if the access manager is allowed to finish itsmobility event procedure without informing the session manager that theaccess of the wireless communication device is being transferred and ifso finish the mobility event procedure without informing the sessionmanager that the access of the wireless communication device is beingtransferred.

With the invention, the one or more UPFs serving the wirelesscommunication device in the first site is advantageously provided withinformation identifying the target access point and informationidentifying the wireless communication device by the access managerwithout passing the central control plane in the second site.

This will have as a consequence that the access manager can finish thehandover procedure without informing the session manager of the centralcontrol plane that the access of the wireless communication device isbeing transferred from the source base stationc to the target basestation, and the number of processing steps is advantageously reduced,thereby also ensuring that strict latency requirements are met byshortcutting unnecessary signaling and processing.

Reduced number of processing steps is further preferred both from alatency and energy consumption view.

An additional benefit of the proposed solution is that processing isdistributed over multiple sites. An operational failure of a node (e.g.a computer or server) in the central site would typically affect severalusers while a similar failure in the proposed distributed solution onlyaffects those users connected to the non-operational computer on thespecific site.

In an embodiment, the information indicating if the access manager isallowed to finish its mobility event procedure without informing thesession manager that the access of the wireless communication device isbeing transferred is acquired from the session manager arranged in thecontrol plane of the second site .

In an embodiment, the information indicating if the access manager isallowed to finish its mobility event procedure without informing thesession manager is fetched from a local storage.

In another embodiment, the information has been previously received fromthe session manager upon performing a Protocol Data Unit (PDU) sessionestablishment procedure for the wireless communication device.

In a further embodiment, the access manager further acquires informationregarding which one or more UPFs serving the wireless communicationdevice should be provided with information identifying the target accesspoint and information identifying the wireless communication device.

The UPF information may again be fetched from a local storage, the UPFinformation having been previously received from the session managerupon performing a PDU session establishment procedure for the wirelesscommunication device.

In a further embodiment, the access manager submits a target accesspoint identifier and a wireless communication device identifier directlyto the one or more UPFs for informing about the mobility event.

In still an embodiment, the UPFs are informed in that the access managersubmits a target access point identifier and a wireless communicationdevice identifier to a User Context Database (UCD), located in thecontrol plane of the at least one first site, the UCD informing acontrol plane plugin of the at least one first site, which pluginsubmits the target access point identifier and the wirelesscommunication device identifier directly to the one or more UPFs.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 illustrates an EPC network architecture being the core network ina LTE communication system;

FIG. 2 shows a prior art 5G core network architecture;

FIG. 3 shows a signalling diagram illustrating handover of a UE in thesystem of FIG. 2;

FIG. 4 illustrates a 5G core network architecture as proposed in anembodiment;

FIG. 5 shows a signalling diagram illustrating handover of a UE in thesystem of FIG. 4; and

FIG. 6 illustrates an access manager according to an embodiment.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided byway of example so that this disclosure will be thorough and complete,and will fully convey the scope of the invention to those skilled in theart. Like numbers refer to like elements throughout the description.

FIG. 1 illustrates an EPC network architecture being the core network ina LTE communication system, and has previously been discussed in detail.

FIG. 2 shows a 5G core network architecture previously proposed by oneof the inventors in “Novel Core Network Architecture for 5G Based onMobile Service Chaining” (by Roeland and Fu).

This is a functional architecture and may run on a platform that may bedistributed over multiple sites in an operator's network, like adistributed cloud. In an implementation different components could bevirtualized and may be combined.

Like EPC, the architecture is divided into a control plane and a userplane. A mobile device 10 communicates with the control and user planevia one or more Access Networks (AN) 11, e.g., a novel 5G radio, E-UTRANor even a fixed access. In FIG. 2, it is assumed that the S1 interfacefrom EPC is re-used.

The control plane contains all control plane logic, allowing for astrict separation between control and user plane. The Session Controller(SC) 18 includes an Access Manager (AM) 18 a for controlling the accessof each mobile device connecting to the network. There is one AM foreach supported access technology (e.g. LTE, WiFi). For an LTE access,the AM 18 a would perform the access-specific functions of the MME.

The SC 18 further comprises a Session Manager 18 b for controlling usersessions and creating a service chain for the user. The SC 18 alsocomprises a User Context Database (UCD) 18 c for storing user-specificdata (commonly referred to as “context”). The SC 18 may comprise one ormore plugins 18 d for implementing appropriate functionality. Forinstance, the AM 18 a may be implemented as a plugin.

The UCD 18 c further stores information identifying a current basestation of this user. A plugin can subscribe to certain changes in thisdatabase. For example, a plugin could request to be informed when thecurrent base station for this user changes. If so, an event occurs andthe plugin would be informed accordingly.

A Chain Controller (CC) 19 deals with the setup and maintenance of theservice chain in the user plane. The control plane also contains aLocation Registry (LR) 20, which will be discussed below. Further, thecontrol plane contains the PCRF 16 and HSS 17.

The user plane contains three types of function nodes: ForwardingElement (FE) 21, User Plane Function (UPF) 22 and Internet Protocol (IP)Advertisement Point (IAP) 23.

An FE 21 forwards each packet to one of its ports based on rules it hasreceived from the control plane. An FE 21 may forward a packet throughone or more UPFs 22. An FE 21 is only concerned with the actualforwarding; it does not classify or modify a packet.

A UPF is a service function that processes user plane packets.Processing may include altering the packet's payload and/or header. UPFsare not expected to know topological information regarding the chain,including which other UPFs are in the chain and how to reach them. A UPFmay serve multiple users, and may or may not keep user context.

For example, if the use case is “mobile broadband” then the UPFs neededcould be one or more of: bandwidth limiting, charging, lawfulinterception, parental control, Quality of Service (QoS) handling, etc.Each use case will have a different set of UPFs. In general, each usermay have a different set of UPFs which is referred to as “service chain”or “UPF chain”. Basically, every packet for a user will travel throughthe set of UPFs (“the UPF chain”) for that user.

The IAP 23 is a key component to achieve an anchorless network; i.e. anetwork without a mobility anchor point. Just like a plain IP router, anIAP advertises a range of IP addresses/prefixes towards an outer IPnetwork 15. This may be Internet or an operator-internal network. Asingle IP address/prefix may be advertised by multiple IAPs. If the IPaddress of a specific device is advertised by multiple IAPs, thenpackets for that device can enter the network via any of those IAPs.Similarly, an anchored approach can be achieved by allowing only asingle IAP to advertise the IP address for that device. Each IAP is thuspre-configured with one or more address ranges. It is the control planethat assigns an IP address/prefix to the device upon attachment.

The LR 20 of the control plane is a table of entries, where each entryis a mapping from device IP address/prefix to current device location.The location is the address of the first UPF in the chain, plusoptionally additional location information, e.g., a BS Identifier (ID).When a device 10 moves from one BS to another, the control plane ensuresthat the LR 20 is updated with the new location. An IAP is only used fordownlink packets heading towards the device. For each downlink packet,the IAP 23 performs the following steps: (1) Query the LR 20 based onthe destination IP address of the packet in order to retrieve thelocation; (2) Tag the packet with the location; (3) Forward the packetvia an FE 21 to the first UPF 22 in the service chain as indicated inthe LR reply.

Upon attach of a mobile user, its UPF chain will be established in thatthe SC 18 decides upon the service this user will receive (that is, theset of UPFs this user will be assigned). In practice, this will behandled by interaction between the AM 18 a, SM 181D and UCD 18 ccomprised in the SC 18, as well as with the HSS 17 which stores the userprofile required by the SC 18 for determining the services.Conceptually, the UCD 18 c holds a copy of this user profile plusadditional real-time information. Further, the CC 19 decides where theseUPFs shall run (on which data plane execution nodes). The CC 19 is awareof the topology of the data plane and decides an optimal placement ofUPFs.

This could be very different depending on use case and the given set ofUPFs. For example, in a low-latency use case, the UPFs need to executeclose to the user. In a plain mobile broadband use case, the UPFs mayrun where it is cheapest (which oftentimes is in a big centralized datacenter).

FIG. 3 shows a signalling diagram illustrating user mobility in the formof handover of a UE 10 from a base station to which it currently isconnected (BS_(SRC)) to a target base station to which it is to behanded over (BS_(T)). In FIG. 3, the two base stations are connected toa same local site, which refers to a physical site where certainfunctions of the core network are executed. It can be viewed as anaggregation point located close to the end-user. A central site is, asthe name indicates, a site located at a more central place in anoperator's network.

As can be seen, the UE 10 receives user plane data in the downlink fromthe UPF 22 via the source base station BS_(SRC) and conversely submits,via the source base station BS_(SRC), any user plane data to the UPF 22and on to e.g. a packet data network such as the Internet. After ahandover is completed, the UE 10 receives user plane data in thedownlink via the target base station BS_(T), and submits any user planedata in the uplink via the target base station BS_(T) to the UPF 22 andfurther on to an intended recipient.

Now, after the two base stations BS_(SRC) and BS_(T) initially haveengaged in communication over an X2 interface for initiating thehandover of the UE 10, the BS_(T) submits in step S101 a Path SwitchRequest to the AM 18 a of the SC 18 comprising a target base stationidentifier BS-IDT for instance in the form of an IP address, and anidentifier UE-ID for the UE 10.

In a first alternative, the AM 18 a informs the UPF 22 in step S102 bysubmitting an AM-UPF Update including BS-IDT and UE-ID such that the UPF22 can submit downlink packages to the base station BS_(T) serving theUE 10 after the handover is completed. As is shown in FIG. 3, this maybe followed by a confirmation submitted by the UPF 22.

In a second alternative, the AM 18 a informs the UCD 18 c that ahandover has occurred in step S103 (possibly followed by aconfirmation), thereby submitting BS-IDT and UE-ID to the UCD 18 c. Aspreviously was described, the UCD 18 c stores information identifyingthe current base station for a user, so the AM 18 a updates the UCD 18 cwith the new location of the UE 10. An appropriate plugin can subscribeto certain changes occurring in the UCD 18 c. For example, a plugin 18 dcould request to be informed when the current base station for this userchanges. If so, an event occurs and the plugin 18 d would be informedaccordingly is illustrated in the Event message received in step S104.As a result, the plugin 18 d submits a UPF Update Request to the UPF 22in step S105 comprising a target base station identifier (here denotedUPF-Data), and an identifier UE-ID for the UE 10.

Thereafter, in case of handover, any UPFs in the current UPF chain mustbe informed about the handover and the new base station BS_(T) to whichthe UE 10 is handed over, i.e. about any target base station identifierBS-ID_(T)/UPF-Data, and UE identifier UE-ID.

Hence, the AM 18 a submits a message named Inform UE Moved in step S106to the SM 18 b, which in its turn sends a Graph Update Request to the CC19 in step S107, and the CC 19 submits a Chain Update Request to the FE21 and the UPF 22 in step S108, which replies with a Chain UpdateAcknowledge to the CC 19 via the FE 21 in step S109. The CC19 in itsturn submits a Graph Update Acknowledge in step S110 to the SM 18 b,which finally sends an Acknowledgement in step S111 to the AM 18 a.

It is noted that steps S107-S110 may have to be performed for all FEsand UPFs in the UPF chain.

To confirm the handover of the UE 10 from the source base stationBS_(SRC) to the target base station BS_(T), the AM 18 a submits a PathSwitch Request Acknowledgement containing the UE-ID in step S112 to thetarget base station BS_(T), which finally sends a Release Resourcemessage to the source base station BS_(SRC) in step S113.

The proposed 5G architecture is flexible in regard to the site or siteswhere the control plane and data plane executes. It would be possible toplace all control plane and user plane functionality in a central site.This may be an attractive scenario when processing at large centralsites is cheaper than processing at smaller local sites. It would alsobe possible to place all control plane and user plane functionality in alocal site. This may be attractive when low latency towards the user isrequired.

More advanced scenarios are also possible. For example, user plane andcontrol plane may execute at different sites. Furthermore, it ispossible that the user plane is distributed over multiple sites, or thatthe control plane is distributed, or both; a great variety of scenariosare possible. Placement policies that may be taken into account are, asmentioned above, latency, processing cost, bandwidth cost, etc.

In the following, a scenario is envisaged where it is desirable to splitthe control plane, i.e. where one part of the control plane is executedon a central site and the remaining part of the control plane isexecuted on local sites. Use cases that would benefit from this are:

-   -   use cases where some UPFs and plugins are processed at a central        site and at the same time other UPFs and plugins are processed        at a local site. One such use case could be vehicle-to-network        communication where latency-sensitive UPFs (e.g. information        to/from the vehicle about its current surrounding and required        processing in the network related to that information) are        deployed at local sites and non-latency-sensitive UPFs (e.g.        management, monitoring, logging, firmware upgrade, etc.) are        deployed at a central site for economic reasons, and    -   use cases which are latency-sensitive (e.g. augmented reality,        virtual reality) and have all UPFs processed at a local site        while user specific data and operational information are stored        at a central site due to specific deployment, administrative or        economic reasons.

One likely deployment scenario is to have a centrally deployed controlplane and a distributed user plane. When such deployment is made in theabove mentioned latency-sensitive use cases, then this causesunnecessary delays and processing overhead when a UE relocates betweentwo base stations connected to the same local site. The followingproblems have been identified for those use cases:

-   -   extra signaling delay; if mobility signaling is sent from the        base station (access network) via an SC-AM in the local site to        an SC-SM located in the central site, although the handover is        performed in the local site, this causes extra signaling delay,        and    -   additional processing requirements; if all UPFs for a user are        located at the local site and the handover is local to the site,        then processing steps S106-S111 in FIG. 3 are not needed. They        will not result in any changes, only extra processing load and        energy consumption.

FIG. 4 illustrates a 5G core network architecture as proposed in anembodiment, FIG. 4 showing a deployment of the logical architecture ofFIG. 2.

As can be concluded from FIG. 4, the core network control plane is inthis particular exemplifying embodiment distributed over two remotelylocated sites; a first site referred to as a local site 30, and a secondsite 40 referred to as a central site.

Similar to the core network of FIG. 2, the architecture is divided intoa control plane and a user plane. In this embodiment, the mobile device10 communicates with the local control plane and the user plane locatedin the first site 40, via one or more ANs 11, e.g., a novel 5G radio,E-UTRAN or even a fixed access, connected to the local site 30.

Like in FIG. 2, the SC 18 includes an AM 18 a for controlling the accessof the mobile device 10 connecting to the core network. There is one AMfor each supported access technology (e.g. LTE, WiFi). For an LTEaccess, the AM 18 a would perform the access-specific functions of theMME.

The SC 18 further comprises an SM 18 b for controlling user sessions andcreating a service chain for the user, and a UCD 18 c for storinguser-specific data and information identifying a current base station ofthis user. A plugin 18 d can subscribe to certain changes in thisdatabase. The SC 18 may comprise one or more plugins for implementingappropriate functionality. For instance, the AM 18 a may be implementedas a plugin.

In the deployment illustrated with FIG. 4, the SC 18 is distributed overthe local site 30 and the central site 40, where the SM 18 b is arrangedin the central site 40, while the AM 18 a and the UCD 18 c is arrangedin the local site 30.

Further in the deployment of FIG. 4, the CC 19—which manages the setupand maintenance of the service chain in the user plane—has beendistributed where a Central Chain Controller 19 a (CCC) is arranged inthe central control plane while a Local Chain Controller 19 b (LCC) isarranged in the local control plane. Even though not shown in FIG. 4,the central control plane also contains the LR, the PCRF and the HSSillustrated and discussed with reference to FIG. 2.

The FE 21 forwards each packet to one of its ports based on rules it hasreceived from the control plane. An FE 21 may forward a packet throughone or more UPFs 22. An FE 21 is only concerned with the actualforwarding; it does not classify or modify a packet. Each use case willhave a different set of UPFs and every packet for a user will travelthrough the set of UPFs (“the UPF chain”) for that user. As previouslydiscussed, the IAP 23 enables a network without a mobility anchor point.

The FE 21 is connected to LCC 19 b in the local control plane and to theUPF 22. Advantageously, in this embodiment the AM 18 a in the localcontrol plane is configured to determine whether an “optimized localhandover” is allowed to be performed, as will be described in moredetail in the following.

A typical site structure of today complies with the following hierarchy:

-   -   1. Lowest in the hierarchy is a base station site. It hosts the        base station hardware and software.    -   2. Then follows an aggregation site. It is used on transport        level to aggregate traffic from multiple base station sites.    -   3. Next in the hierarchy is a regional site, which spans e.g. a        greater metropolitan area, where parts of the core network may        run.    -   4. Last is the national site. Typically are just a few of these        in a country. Here the rest of the core network runs.

The site structure may also differ per operator. Small operators mayskip e.g. the regional sites. Very large operators may have additionallevels in the hierarchy. The hierarchy often also differs between urbanand rural areas. There is no standard site hierarchy.

With reference to the 5G core network of FIG. 4, the local site 30 couldconstitute an aggregation site or regional site while the central sitecould constitute a regional or national site.

FIG. 5 shows a signalling diagram illustrating a UE 10 undergoing amobility event in the form of a handover of the UE 10 from a basestation to which it currently is connected (BS_(SRC)) to a target basestation to which it is to be handed over (BS_(T)), where the two basestations are connected to the same local site 30.

Now, after the two base stations BS_(SRC) and BS_(T) initially haveengaged in communication over an X2 interface for initiating thehandover of the UE 10, the BS_(T) submits in step S201 informationregarding the mobility event in the form of a Path Switch Request to theAM 18 a of the SC 18 comprising a target base station identifierBS-ID_(T) in the form of an IP address, and an identifier UE-ID for theUE 10.

As a result of the Path Switch Request, one or more UPFs 22 serving themobile communication device must, as previously has been discussed withreference to the signaling diagram of FIG. 3, be provided withinformation BS-ID_(T) identifying the target base station BS_(T) as wellas information UE-ID identifying the UE 10. It is noted that only UPFsbeing a part of the service chain for this particular event is providedwith the information; the UE 10 may very well be connected to other UPFsfor receiving other services, which other UPFs not necessarily need tobe provided with the information that a mobility event has occurred.

With the invention, this required information will advantageously beprovided by the AM 18 a to the UPFs 22 without passing the centralcontrol plane in the second site 40.

In a first alternative, the AM 18 a informs the UPF 22 directly in stepS202 by submitting an AM-UPF Updated including BS-ID_(T) and UE-ID suchthat the UPF 22 can submit downlink packages to the base station BS_(T)serving the UE 10 after the handover is completed. As is shown in FIG.5, this may be followed by a confirmation submitted by the UPF 22.

In a second alternative, the AM 18 a informs the UCD 18 c that ahandover is to occur in step S203 (possibly followed by a confirmation).As previously was described, the UCD 18 c stores information identifyingthe current base station for a user, so the AM 18 a updates the UCD 18 cwith the new location of the UE 10. An appropriate plugin 18 d cansubscribe to certain changes occurring in the UCD 18 c.

For example, the plugin 18 d could request to be informed when thecurrent base station for this user changes. If so, an event occurs andthe plugin 18 d would be informed accordingly as is illustrated in theEvent message received in step S204.

As a result, the plugin 18 d submits a UPF Update Request to the UPF 22in step S205 comprising a target base station identifier (here denotedUPF-Data), and an identifier UE-ID for the UE 10.

Further, in step S206, the AM 18 a acquires information indicating ifthe AM 18 a is allowed to finish its mobility event procedure—in thisparticular example being a handover procedure—without informing the SM18 b in the central control plane located in the second site 40 that theaccess of the UE 10 is being transferred. In FIG. 4, this is expressedas an “optimized local handover”, a local handover being a handoverbetween two base stations both connected to the first site 30.

Now, if this is the case, the AM 18 a finishes, in step S207, thehandover procedure that was initiated by the Path Switch Requestreceived in step S201, without informing the SM 18 b of the centralcontrol plane that the access of the UE 10 is being transferred from thesource base station BS_(SRC) to the target base station BS_(T).

This is highly advantageously, as there is no need to for the corenetwork to perform the steps denoted S106-S113 (to comply with thenotation used in FIG. 3), which were described in detail in FIG. 3.

In an embodiment, the optimized local handover is allowed if the AM 18 ais located in the same site, in this particular example the first site30, as the UPF(s) being informed of the handover in steps S202 or S205.

In an embodiment, the AM 18 a is provided with the information in stepS206 as to whether it may finish the handover procedure in step S207 bythe SM 18 b in the central control plane, for instance already during aProtocol Data Unit, PDU, session establishment procedure undertaken whenthe UE 10 sets up a connection with a PDU network 15 via the corenetwork.

As an example, the UE 10 will, via a base station in the AN 11, submitto the AM 18 a a conventional PDU Connection Request indicating AccessPoint Name (APN) of the packet data network 15 with which it desires toconnect. The AM 18 a will in its turn submit a New Session Request tothe SM 18 b, and after the required control and user plane processinghas been performed to set up the PDU session, the SM 18 b submits a NewSession Acknowledgement to the AM 18 a. In an embodiment, the NewSession Acknowledgement is configured to comprise the information as towhether the AM 18 a is allowed to finish the handover procedure in stepS207 or not. The AM 18 a stores the information locally for subsequentaccess. Hence in step S206, the AM 18 a fetches the locally storedinformation. The SM 18 b will only send that information when there areno UPFs in other sites (other than the local site 30) that needs to bemade aware about UE location updates.

Further, the New Session Acknowledgement may be extended with furtherinformation, e.g. “optimized local handover allowed” but only for acertain period, or only for UE handover between certain base stations.Other additions could be that optimized local handover is allowed, butafter a certain time or certain number of handovers the new BS ID shallstill be reported to the SM 18 b.

The proposed solution allows for a split SC deployment wherelatency-sensitive functionality is located close to the end-user, i.e.in local site 30, and non-latency-sensitive SC functionality is locatedin central site 40, i.e. it allows for different deployment options ofthe control plane based on operator requirements.

The SC functionality of the local site 30 is related to local mobilityhandling of the UE 10 moving between access points connected to the samelocal site 30. The decision to approve or not approve an optimizedhandover can be taken locally and does not need any support from thecentral control plane functionality.

For certain use cases latency requirements are very strict and are onlyachieved when the user plane and (at least parts of) the control planeare both deployed at local sites, i.e. close to the end-user. Theproposed solution is provided by the invention ensures that the moststrict latency requirements are met by shortcutting unnecessarysignaling and processing.

Reduced number of processing steps is preferred both from a latency andenergy consumption view. The proposed solution makes it possible toreduce the number of processing steps.

An additional benefit of the proposed solution is that processing isdistributed over multiple sites. An operational failure of a node (e.g.a computer or server) in the central site would typically affect severalusers while a similar failure in the proposed distributed solution onlyaffects those users connected to the non-operational computer on thespecific site.

In a further embodiment, the AM 18 a acquires information as to whichUPF(s) 22 should be informed of the handover in steps S202 or S205.

A number of options is envisaged; the AM 18 a may be informed about therelevant UPF(s) 22 to notify that a mobility event has occurred by theSM 18 b, for instance already during a PDU session establishmentprocedure undertaken when the UE 10 sets up a connection with a PDUnetwork 15 via the core network, in which case the information is storedlocally at the AM 18 a as previously discussed.

Alternatively, there is a pre-configuration in the AM 18 a on whichUPF(s) 22 to inform abut the handover.

In a further alternative embodiment, the AM 18 a stores the mobilityevent information in the UCD 18 c, in which case the UPF(s) 22 that areinterested subscribe to UCD events and is informed of the handover. Thiswould correspond to alternative 2 in FIG. 4.

With reference to FIG. 6, the steps of the method performed by the AM 18a according to embodiments are in practice performed by a processingunit 50 embodied in the form of one or more microprocessors arranged toexecute a computer program 51 downloaded to a suitable storage volatilemedium 52 associated with the microprocessor, such as a Random AccessMemory (RAM), or a non-volatile storage medium such as a Flash memory ora hard disk drive. The processing unit 50 is arranged to cause the AM 18a to carry out the method according to embodiments when the appropriatecomputer program 50 comprising computer-executable instructions isdownloaded to the storage medium 52 and executed by the processing unit50. The storage medium 52 may also be a computer program productcomprising the computer program 51. Alternatively, the computer program51 may be transferred to the storage medium 52 by means of a suitablecomputer program product, such as a Digital Versatile Disc (DVD) or amemory stick. As a further alternative, the computer program 31 may bedownloaded to the storage medium 52 over a network. The processing unit50 may alternatively be embodied in the form of a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), a complex programmable logicdevice (CPLD), etc.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedpatent claims.

1-18. (canceled)
 19. A method performed by an access manager oftransferring data in a wireless communication system comprising acontrol plane distributed over at least one first site and over at leastone second site, wherein a session manager is arranged in the controlplane of the second site and the access manager is arranged in thecontrol plane of the first site, the first site being remote from thesecond site and located physically closer to a radio access network ofthe wireless communication system, comprising: receiving, from a targetbase station to which a wireless communication device is to be handedover, a path switch request where access of the wireless communicationdevice is being transferred from a source access point to a targetaccess point, the access points being connected to said at least onefirst site; further being characterized in comprising: providing one ormore User Plane Functions, UPFs, serving the wireless communicationdevice with information identifying the target access point andinformation identifying the wireless communication device, wherein theinformation is provided to the one or more UPFs without passing thecontrol plane of the second site; and acquiring, from the sessionmanager, information indicating if the access manager is allowed tofinish its path switch request procedure without informing the sessionmanager that the access of the wireless communication device is beingtransferred; and if so finishing the path switch request procedurewithout informing the session manager that the access of the wirelesscommunication device is being transferred.
 20. The method of claim 19,wherein the step of acquiring information comprises: acquiringinformation indicating if said one or more UPFs serving the wirelesscommunication device are located in the at least first site.
 21. Themethod of claim 19, wherein the step of acquiring information comprises:requesting the information from the session manager arranged in thecontrol plane of the second site.
 22. The method of claim 19, whereinthe step of acquiring information comprises: fetching the informationindicating if the access manager is allowed to finish its path switchrequest procedure without informing the session manager from a localstorage, the information indicating if the access manager is allowed tofinish its path switch request procedure without informing the sessionmanager having been previously received from the session manager. 23.The method of claim 19, wherein the step of acquiring informationcomprises: acquiring information regarding which one or more UPFsserving the wireless communication device should be provided withinformation identifying the target access point and informationidentifying the wireless communication device.
 24. The method of claim19, wherein the step of providing one or more UPFs with informationcomprises: submitting a target access point identifier and a wirelesscommunication device identifier directly to the one or more UPFs. 25.The method of claim 19, wherein the step of providing one or more UPFswith information comprises: submitting a target access point identifierand a wireless communication device identifier to a User ContextDatabase, UCD, located in the control plane of the at least one firstsite, the UCD informing a control plane plugin of the at least one firstsite, which plugin submits the target access point identifier and thewireless communication device identifier directly to the one or moreUPFs.
 26. An access manager configured to transfer data in a wirelesscommunication system comprising a control plane distributed over atleast one first site and over at least one second site, wherein asession manager is arranged in the control plane of the second site andthe access manager is arranged in the control plane of the first site,the first site being remote from the second site and located physicallycloser to a radio access network of the wireless communication system,the access manager comprising a processing unit and a memory, saidmemory containing instructions executable by said processing unit,whereby said access manager is operative to: receive information), froma target base station to which a wireless communication device is to behanded over, regarding a path switch request where access of thewireless communication device is being transferred from a source accesspoint to a target access point, the access points being connected tosaid at least one first site; further being characterized in beingoperative to: provide one or more User Plane Functions, UPFs, servingthe wireless communication device with information identifying thetarget access point and information identifying the wirelesscommunication device, wherein the information is provided to the one ormore UPFs without passing the control plane of the second site; andacquire, from the session manager, information indicating if the accessmanager is allowed to finish its path switch request procedure withoutinforming the session manager that the access of the wirelesscommunication device is being transferred; and if so finish the pathswitch request procedure without informing the session manager that theaccess of the wireless communication device is being transferred. 27.The access manager of claim 26, further being operative to, whenacquiring the information: acquire information indicating if said one ormore UPFs serving the wireless communication device are located in theat least first site.
 28. The access manager of claim 26, further beingoperative to, when acquiring the information: request the informationfrom the session manager arranged in the control plane of the secondsite.
 29. The access manager of claim 26, further being operative to,when acquiring the information: fetch the information indicating if theaccess manager is allowed to finish its path switch request procedurewithout informing the session manager from a local storage, theinformation indicating if the access manager is allowed to finish itspath switch request procedure without informing the session managerhaving been previously received from the session manager.
 30. The accessmanager of claim 26, further being operative to, when acquiring theinformation: acquire information regarding which one or more UPFsserving the wireless communication device should be provided withinformation identifying the target access point and informationidentifying the wireless communication device.
 31. The access manager ofclaim 26, further being operative to, when providing the one or moreUPFs with information: submit a target access point identifier and awireless communication device identifier directly to the one or moreUPFs.
 32. The access manager of claim 26, further being operative to,when providing the one or more UPFs with information: submit a targetaccess point identifier and a wireless communication device identifierto a User Context Database, UCD, located in the control plane of the atleast one first site, the UCD informing a control plane plugin of the atleast one first site, which plugin submits the target access pointidentifier and the wireless communication device identifier directly tothe one or more UPFs.
 33. A method performed by an access manager oftransferring data for a wireless communication system having a controlplane distributed over at least one first site and over at least onesecond site wherein a session manager is arranged in the control planeof the second site and an access manager is arranged in the controlplane of the first site, the first site being remote from the secondsite and located physically closer to a radio access network of thewireless communication system, a non-transitory computer-readablestorage medium comprising a computer program product includinginstructions to cause at least one processor to: receive, from a targetbase station to which a wireless communication device is to be handedover, a path switch request where access of the wireless communicationdevice is being transferred from a source access point to a targetaccess point, the access points being connected to said at least onefirst site; further being characterized in being operative to: provideone or more User Plane Functions, UPFs, serving the wirelesscommunication device with information identifying the target accesspoint and information identifying the wireless communication device,wherein the information is provided to the one or more UPFs withoutpassing the control plane of the second site; and acquire, from thesession manager, information indicating if the access manager is allowedto finish its path switch request procedure without informing thesession manager that the access of the wireless communication device isbeing transferred; and if so finish the path switch request procedurewithout informing the session manager that the access of the wirelesscommunication device is being transferred.